1. Technical Field
The disclosure relates to optical microscopy. In particular, the disclosure relates to a far-field optical microscope with a nanometer-scale resolution based on the in-plane image magnification by surface plasmon polaritons.
2. Description of the Prior Art
Far-field optical microscopy remains invaluable in many fields of science, even though various electron and scanning probe microscopes have long surpassed it in resolving power. The main advantages of the far-field optical microscope are the ease of operation and direct sample visualization. Unfortunately, the resolution of a regular optical microscope is limited by the wavelength of visible light. The reason for the limited resolution is diffraction and, ultimately, the uncertainty principle: a wave can not be localized much tighter than half of its vacuum wavelength λ/2.
Immersion microscopes introduced by Ernst Abbe in the 19th century have slightly improved resolution on the order of λ/2n because of the shorter wavelength of light λ/n in a medium with refractive index n. However, immersion microscopes are limited by the small range of refractive indices n of available transparent materials. It was believed that the only way to achieve nanometer-scale spatial resolution in an optical microscope is to beat diffraction, and detect evanescent optical waves in very close proximity to a studied sample using a scanning near-field optical microscope. Although many fascinating results are obtained with near-field optics, such microscopes are not as versatile and convenient to use as regular far-field optical microscopes. For example, an image of a near-field optical microscope is obtained by point-by-point scanning, which is an indirect and a rather slow process.
However, it has been realized that a dielectric droplet on a metal surface which supports propagation of surface plasmons (or surface plasmon polaritons) may have an extremely large effective refractive index as seen by these modes (see I. I. Smolyaninov, Surface plasmon toy-model of a rotating black hole, New Journal of Physics, vol. 5, pages 147.1-147.8, October 2003, the contents of which are incorporated herein by reference). The properties of surface plasmons and convenient ways to excite them are described in detail in H. Raether, Surface Plasmons, Springer Tracts in Modern Physics, vol. 111, Springer, Berlin, 1988.
Accordingly, it is an aspect of the present disclosure to describe a far-field optical microscope capable of reaching nanometer-scale resolution using the in-plane image magnification by surface plasmon polaritons based on the optical properties of a metal-dielectric interface that may provide extremely large values of the effective refractive index neff up to 103 as seen by surface polaritons, and thus the diffraction limited resolution can reach nanometer-scale values.